Recently, the reclamation of waste plastics is of great interest throughout the world in the view of environmental protection and energy reclamation, and is studied in a variety of manners. As one field of such a waste plastic reclamation, the recovery of fuels from waste plastics is recognized.
The conventional methods for the recovery of fuels from waste plastics mostly enable the production of kerosene, diesel oil and/or a mixture thereof. However, due to technical problems associated with a process and equipment, such as a pre-treatment of the waste plastic raw material, a cracking, a fractionation, and a refining, etc., there is no report for the production of gasoline, in particular for automobiles, using the waste plastics.
Gasoline generally designates volatile, combustible liquid hydrocarbons obtained by the reforming distillation, polymerization, catalytic cracking, and alkylation, etc. of crude oil. In most countries, octane number, distillation property, and allowable contents of harmful substances, such as lead or sulfur components, for gasoline, are provided under the law. In particular, the octane number and the distillation property are the most important quality standards of a fuel for an automobile internal combustion engine. Gasoline produced in an oil refinery conforms to the quality standards provided under the law, by combining a low- or high-boiling fraction of a low or high octane number to a mixed product of a product from a Fluid Catalyst Cracking Unit (FCCU) and a product resulted from the reforming of a high-boiling fraction from the hydrocracking of naphtha produced in the atmospheric distillation of crude oil. For this reason, the use of waste plastic for production of gasoline is difficult to meet with the quality standards.
Waste plastics, that are polymers of a high molecular weight, have a problem in that, upon a simple thermal decomposition, they produce mainly a wax fraction, with little or no production of gasoline, kerosene, and light oil, due to a decomposition property thereof.
Therefore, as solutions for the above problem, there are proposed thermal decomposition methods using a solid acid as a catalyst. A drawback with these methods is, however, that C1 to C3 waste gases, and a mixed oil fraction of C8 to C25 kerosene and diesel oil are mainly produced, while an oil fraction of 4 to 25 carbon atoms which is main component is not produced in a good yield. As a result, the reclamation of waste plastic is limited only to the mixed oil.
In addition to this drawback, the above thermal decomposition method has another problem in that coke and polymeric materials, that are formed during the catalytic cracking of waste plastic melt, directly form a barrier to a catalyst surface, such that a serious catalytic poison phenomenon occurs, thereby reducing rapidly the catalyst activity. For this reason, a method is used in which simply thermally decomposed gaseous oil is partially cracked and isomerized by passing the gaseous oil through a fixed bed reactor filled with a catalyst. However, this method has a problem in that, since the temperature in the fixed bed is lower than that in the thermal decomposition, a reaction conversion is seriously limited. Moreover, in this method, the regeneration and the replacement of the catalyst due to the catalytic poison phenomenon require significant cost, and are also very complicated. Owing to these disadvantages, this method is limited in its application to the commercial facility. Additionally, this method is relatively low in production of gasoline oil fraction, and thus was not believed to be suitable for the production of gasoline.